This invention relates to adjustable manhole cover supports for emplacing over and raising the grade of an existing manhole cover receiving structure.
For simplicity the terms "existing manhole cover receiving structure" and "manhole cover" herein are used to refer to the existing, i.e., fixed in-place frame or other existing seating receptacle for a removable cover or grating that covers an access hole (i.e., hand hole, tool hole, manhole, catch basin or the like), and that cover or grating ordinarily is intended to bear vehicular traffic. The term "manhole cover support" or simply "cover support" here means a structure that fits over the existing manhole cover receiving structure, raises its grade, and thereby accommodates a cover or grating at the new grade. Advantageously, the cover or grating is the same one that was used at the lower grade. The access hole covered is a utility enclosure serving, e.g., an electric, gas, water, sewer or storm drainage system.
Ordinarily the instant cover support finds its use when a roadway such as a street or highway is resurfaced with an added layer of paving material, typically asphalt concrete, or otherwise is overlaid or repaved to establish a higher grade. It then is advantageous to mount the inventive cover support atop the existing manhole receiving structure. Relevant prior art on manhole cover supports and manhole cover frames can be found in U.S. Pat. Nos. 4,281,944, 4,236,358, 3,968,600, 3,773,428, 4,097,171, 4,302,126, 3,891,337 and 1,987,502. The first four of these are for inventions of the applicant.
Axle loads up to 40,000 pounds must be resisted by many of these cover supports as well as serious impact loads from vehicles and snow plows, a variety of temperature effects, steam leaks, spillage, etc., without permitting a hazardous dislocation of the cover support or its cover. Often it is desirable also to cushion the cover a bit for resisting wear or reducing noise, or to seal the cover and its cover support against a substantial and possibly overloading infiltration of surface water, e.g., storm drainage that otherwise would enter a sanitary sewer system at various manhole locations. Adjustability of the cover support in peripheral dimension and height also is important for accommodating the wide range of specifications to be met.
Clearly the resistance to displacement from traffic loading and impact is a paramount concern and a most general one. The supports often contain some reasonably thin (0.1 inch or less) elements such as sheet steel elements. These can include upwardly projecting cover keeper wall portions, flanging, and bases. Such thin keeper portions can be fitted into an existing manhole cover frame and, normally, still leave a large enough opening at the new-grade to accommodate the same old cover or lid which was used on the existing frame. The lighter weight elements also can be effective for economy and/or ease of manufacture, handling an installation. However, a relatively low weight of the cover support, as compared to the usually thick cast iron fixture on which it is to rest, makes it a candidate for displacement in service. This is true even when a cover support can be expanded against the rising shoulder of a receiving structure such as a manhole cover frame in the manner of various prior art cover supports such as those in U.S. Pat. Nos. 4,281,944, 4,236,358, 4,097,171 and 4,302,126, noted above. polygonal, e.g., quadrangular, cover supports can be especially prone to such displacement. Where the retention is mainly due to the weight of a cover and its support, displacement is even more of a risk.
The instant support can be made especially highly resistant to displacement and dislodgement in service without being made ponderous in weight, even when it has no mechanical fastening to the receiving structure. Thus, while the present cover support can be made to incorporate conventional structural or mechanical holddown means that are integral with it or easily attached, the cover support also can do a good job of holding in (being retained in the existing receiving structure while in service) simply by friction alone, and this not necessarily (but often desirably) with the use of any friction-enhancing retention member.
Additionally, the present support is polygonal and adjustable. It can be adapted readily to sealing off against water infiltration and to cushioning the cover. Furthermore, its stiffness can be made unusually high while its weight can be kept low.
No previously proposed manhole cover supports are known by the inventor to have these very desirable advantages, let alone the capability of combining several or all of them in a cover support in a practical manner.